Jack Nicholson used to be the definitive Joker but now he's become very underrated.

Many people say he's just playing himself, which isn't a fair criticism. I thought the look, the laugh, the voice and the mannerisms were all Joker. Plus, he also had to play Jack Napier as well and make his performance different to that when he 'becomes' Joker. In that sense, he was good if not better than Ledger.